FFMPEG Merge Multiple Videos: No Audio Source for one of them - audio

Question

I've written a node.js script to merge multiple video files into a single file. I've encountered a scenario in which no audio is provided for one of the input video files.
I first executed ffprobe so that I can access what I'll refer to as the "video file spec". In this scenario, I created a basic module to help me better understand my problem:
Evaluation from all processes: [
{
fileName: 'input-0.mp4',
isVideoAvailable: true,
isAudioAvailable: false,
width: 1920,
height: 1080,
sampleRateAspectRatio: '1/1',
audioVolume: 1,
duration: '13.140000'
},
{
fileName: 'input-1.mp4',
isVideoAvailable: true,
isAudioAvailable: true,
width: 1920,
height: 1080,
sampleRateAspectRatio: '1/1',
audioVolume: 1,
duration: '17.160000'
},
{
fileName: 'input-2.mp4',
isVideoAvailable: true,
isAudioAvailable: true,
width: 1920,
height: 1080,
sampleRateAspectRatio: '1/1',
audioVolume: 1,
duration: '20.280000'
},
{
fileName: 'input-3.mp4',
isVideoAvailable: true,
isAudioAvailable: true,
width: 1920,
height: 1080,
sampleRateAspectRatio: '1/1',
audioVolume: 1,
duration: '19.020000'
},
{
fileName: 'input-4.mp4',
isVideoAvailable: true,
isAudioAvailable: true,
width: 1920,
height: 1080,
sampleRateAspectRatio: '1/1',
audioVolume: 1,
duration: '9.480000'
}
]
This next block of code are the parameters that I've actually hard-coded in this case. The screen resolution and aspect ratio are manually set, as I discovered differing settings with each video I have been processing. These parameters allow FFMPEG to execute successfully under normal circumstances:
let ffmpegParameters = [
'-i',
'input-0.mp4',
'-i',
'input-1.mp4',
'-i',
'input-2.mp4',
'-i',
'input-3.mp4',
'-i',
'input-4.mp4',
'-f',
'lavfi',
'-t',
'0.1',
'-i',
'anullsrc',
'-filter_complex',
'[0:v]scale=1920:1080,setsar=1/1[v0];[0:a]volume=1.0[a0];[1:v]scale=1920:1080,setsar=1/1[v1];[1:a]volume=1.0[a1];[2:v]scale=1920:1080,setsar=1/1[v2];[2:a]volume=1.0[a2];[3:v]scale=1920:1080,setsar=1/1[v3];[3:a]volume=1.0[a3];[4:v]scale=1920:1080,setsar=1/1[v4];[4:a]volume=1.0[a4];[v0][a0][v1][a1][v2][a2][v3][a3][v4][a4]concat=n=5:v=1:a=1[v][a]',
'-map',
'[v]',
'-map',
'[a]',
'-c:v',
'libx264',
'-vsync',
'2',
'output.mp4'
]
A comment from a different thread suggested to supply a dummy audio in cases such as mine. I've added that to no prevail:
'-f',
'lavfi',
'-t',
'0.1',
'-i',
'anullsrc',
I do not know how to adjust the complex filter to account for my situation of the first video containing no audio. I've included the entire log below:
Logs:
ffmpeg version git-2020-02-03-1c15111
Copyright (c) 2000-2020 the FFmpeg developers
built with Apple clang version 11.0.0 (clang-1100.0.33.8)
configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-appkit --enable-avfoundation --enable-coreimage --enable-audiotoolbox
libavutil 56. 38.100 / 56. 38.100
libavcodec 58. 67.100 / 58. 67.100
libavformat 58. 37.100 / 58. 37.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 73.100 / 7. 73.100
libswscale 5. 6.100 / 5. 6.100
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input-0.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.37.100
Duration: 00:00:14.80, start: 1.620000, bitrate: 1499 kb/s
Stream #0:0(und): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1498 kb/s, 25 fps, 25 tbr, 1200k tbn, 2400k tbc (default)
Metadata:
handler_name : VideoHandler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'input-1.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.37.100
Duration: 00:00:18.48, start: 0.000000, bitrate: 977 kb/s
Stream #1:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1440x876 [SAR 1:1 DAR 120:73], 903 kb/s, 15.21 fps, 16.67 tbr, 16k tbn, 32k tbc (default)
Metadata:
handler_name : VideoHandler
Stream #1:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default)
Metadata:
handler_name : SoundHandler
Input #2, mov,mp4,m4a,3gp,3g2,mj2, from 'input-2.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.37.100
Duration: 00:00:22.68, start: 0.000000, bitrate: 1795 kb/s
Stream #2:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1718 kb/s, 29.54 fps, 50 tbr, 16k tbn, 32k tbc (default)
Metadata:
handler_name : VideoHandler
Stream #2:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default)
Metadata:
handler_name : SoundHandler
Input #3, mov,mp4,m4a,3gp,3g2,mj2, from 'input-3.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.37.100
Duration: 00:00:54.60, start:
0.000000, bitrate: 404 kb/s
Stream #3:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1440x876 [SAR 1:1 DAR 120:73], 330 kb/s, 15.24 fps, 16.67 tbr, 16k tbn, 32k tbc (default)
Metadata:
handler_name : VideoHandler
Stream #3:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default)
Metadata:
handler_name : SoundHandler
Input #4, mov,mp4,m4a,3gp,3g2,mj2, from 'input-4.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.37.100
Duration: 00:00:09.36
, start: 0.000000, bitrate: 1794 kb/s
Stream #4:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1717 kb/s, 29.38 fps, 50 tbr, 16k tbn, 32k tbc (default)
Metadata:
handler_name : VideoHandler
Stream #4:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default)
Metadata:
handler_name : SoundHandler
Stream specifier ':a' in filtergraph description [0:v]scale=1920:1080,setsar=1/1[v0];[0:a]volume=1.0[a0];[1:v]scale=1920:1080,setsar=1/1[v1];[1:a]volume=1.0[a1];[2:v]scale=1920:1080,setsar=1/1[v2];[2:a]volume=1.0[a2];[3:v]scale=1920:1080,setsar=1/1[v3];[3:a]volume=1.0[a3];[4:v]scale=1920:1080,setsar=1/1[v4];[4:a]volume=1.0[a4];[v0][a0][v1][a1][v2][a2][v3][a3][v4][a4]concat=n=5:v=1:a=1[v][a] matches no streams.
When I removed the stream specifier [a0], I received a different error:
FFmpeg Video Merge - STDERR: [Parsed_setsar_3 # 0x7f87c7709100] Media type mismatch between the 'Parsed_setsar_3' filter output pad 0 (video) and the 'Parsed_concat_14' filter input pad 1 (audio)
[AVFilterGraph # 0x7f87c7430c00] Cannot create the link setsar:0 -> concat:1
My question is how will the filter-complex value of my parameter list that I have defined be adjusted to deal with that first video, which has no audio?

Answer 1

Stream specifier ':a' in filtergraph description … matches no streams
You are referencing a stream that does not exist. In this case it is due to [0:a]volume=1.0[a0]. You are attempting to select audio from input-0.mp4, but this input has no audio.
Media type mismatch
I don't know your exact command so I can't point out the actual cause, but your video and audio filter labels are likely mixed up somewhere.
Working Example
ffmpeg -i input-0.mp4 -i input-1.mp4 -i input-2.mp4 -i input-3.mp4 -i input-4.mp4 -f lavfi -t 0.1 -i anullsrc=channel_layout=mono:sample_rate=44100 -filter_complex "[0:v]scale=1920:1080,setsar=1/1[v0];[1:v]scale=1920:1080,setsar=1[v1];[2:v]scale=1920:1080,setsar=1[v2];[3:v]scale=1920:1080,setsar=1[v3];[4:v]scale=1920:1080,setsar=1[v4];[v0][5][v1][1:a][v2][2:a][v3][3:a][v4][4:a]concat=n=5:v=1:a=1[v][a]" -map "[v]" -map "[a]" -movflags +faststart output.mp4
Since volume=1 does absolutely nothing you can eliminate that filter.
For the video input without audio pair it with the anullsrc output in concat (as with [v0][5] in the example above).
concat filter will automatically select a common sample rate and channel layout for audio streams, but I still prefer to manually set them in anullsrc so I know for sure what I'm going to get.
Your inputs vary in DAR, so the 1440x876 videos will look squished in the output. You can avoid this by adding scale + crop or pad. Since they all have the same SAR refer to Resizing videos with ffmpeg to fit into static size.
Upscaling is usually not a great idea. Consider downscaling to 1280x720 instead since half the inputs are that size.